Electric ship propulsion



.54 Fans 1. MARTIN AND F H. CLOUGH.

'ELECTRIC SHIP PROPULSION.

APPLICATION FILED MAR. 24, 1921.

1,417,342. Patented y 23, 1922.

2 SHEETS-SHEET l- 48 f'OLES 64 CYCLES 4.9 CYCLES Fig. I

.InVenbbrs I John Mar-tin, Fredr-iok H. clough y Jym' M I Their Attor-fiey.

J. MARTIN AND F. H. CLOUGH.

ELECTRIC SHIP PROPULSION.

APPLICATION FILED MAR.24, 1921.

1,417,342; ented 'y23,1922

2 SHEETS-SHEET 2.

6 POLES 36 FULBS' Invmoorsi John Martin, Frederick H. Clough, y /fi r/r [f ii Their Attorney.

umrso STATES-j Tami OFFICE;

" JOHN m'rm' FREDERICK s, cnouen, air-RUGBY, ENGLAND, assign v have invented certain new and usefu Imship propulsion system in which thereare a' ememr. unc'rmc cours ng, A combust on or i m snin'raornrsxorr. 1'

To all wh'omit may concern: Be it known that we, Jo n: MARTIN and FREDERICK HORTON CLoUeH,1subjects of the ,K in of Great Britain, residing at Rugby,

in t efcounty of Warwiekshire, En land,

provements in Electric Ship Propulsion, of which the followin 'is'a specificat1on.

Our invention re ates to electricjshi ."propulsion, and more particularlyto an e ectric plurality of prime. movers driving alternators at different speeds whereby a plurality of alternating currentjsources of diii'erent frequencies are obtained forthe operation-of driving fmotors located on tl1e propeller.

shafts. v n I I Our. system ofship propulsion is 'part1cu- I -larlyada ted to such service as the propul battle shiphcruisers, where 1t 1s generally desirable tordri've the ship at a sion ofcruising speed but'where at times it should be possible'to drive it at high speed,-1rrespective of economy. It haslbeen proposed in the past .to obtain this'object by PF 'OVId-r ing one or more sets per ship consist ng of two turbine driven alternators achythe a1- ternators in each set being designedto supplydifi'erent frequencies and the ower from these alternators being applie to drive synchronous motors mounted I on the pm pellershafts. In one proposed arrangement,

there are two motors mounted on'each saft with their pole numbers so arranged that ,when the motors are connected 41p 'to their res ective alternators the synchronous speed of oth motors will be'the same. 'When the alternatorsare operating at full speed-this method of operation. givesthe M h power and high speed'condition of thedrive. For

a the low speed'condition the high frequency power necessary at low speed.

alternator'is inactive and the low frequency alternator is connected to'those motors having the greater number of poles, so'that the s nchronous'speed, of these motors is re need in proportion tothe reduction in the frequencyof the source. In this way but one alternator may be used .to su 1y all the conomical running is, however, still-obtained because one alternator is running at itsnormal' full speed and withapproximately normal out-' put. I, I I I In the arrangement described above, difiidrive, where there are two or more I s n that in case power should be is no assurance would not flow between them.

specification together i s own as having/18 poles,

I and 16 of fewer poles,

of the s nchronous as the a ternators 19 and 20.

Matters are so arranged as between the two propeller shafts 11 and 12 that the ro- I ftors of the motors 15 and 16 are always in synchronism whenever the rotors of motors 13 and 14 are in synchronism. In the presmw Yon'x.

specification olLette ra Patent. P a'f e t fl M 23 1 m licatio nua'umnaamn. ser aijno, 46am.

change from 1 w speed drive to high speed 'ljer shafts, hile the propeller shaftsare being driven polenumbers to the ,low frequency source, -1t1s not at all certain that the motors; with the fewer poles. are also in en thesemotors of fewer-poles in para el, there u he object of the present nvention is. to insurethat these circulating currents do not flow when the motors having the fewer poles are con nected to the low frequency source, or, in otherwords, that themotors of fewer poles are synchronized, are synchronized.

For a better understanding of our invent1on, reference is to be'had to the following with the accompany: 1n drawm in which .Fig. 1 is one embo lment, 0 our invention, while .2 shows a modification.

; -;Referring now more in detail to the draw ing, in Fig. 1 we show a air-0f propeller shafts 11 and 12 upon sac of (Which. there is directly mounted a synchronous motor. These synchronous motors are designated the numerals 13 and 1t and are each number is merely taken Also mounted upon the and 12 are another set 0 by wa ofexample driving motors 15 The synchronous. motors 13 and 1 -are p pe I at low speed by the connection of the synchronous motors with the greater whenever the other motors chronism, so

liedto I :es a that :c1rculatin currents 7 although this frope ler shafts 11 forex'ample 36 else,

adapted to be connected by means of switches 17or 18either to an alternator 19 of c0mparatively high'freq'uenc or to an alternator 20 of comparative y These alternators are driven by 'me movers, such as steam turbines 21'and 22; The motors 15 and 16 are adapted to be connected, as for example by means of switch 23, to the low frequency alternator 20. An exciter, 24, driven from any appropriate source is provided to supply the excitation motors 13 and 14 as well low frequency. I

ent instance we accomplish this result by making motors 15 and 16 squirrel cage induction motors. The squirrel cage rotors are preferably so constructed that there are a large number of bars per pole for each pole of the synchronous motors 13 and 14. In this way,'so long as the rotors of the synchronous motors 13 and 14 are in synchronism, these induction motors may be supplied in parallel from a source and no appreciable circulating currents can flow between them. The high frequency source has 64 cycles and the low frequency source has 49 cycles, when the propeller shafts operate at normal high speed. The connections in Fig. 1 show the high speed condition for which purpose switches 17 and 23 are closed, and switch 18 is open. The induction m0- tors 15 and 16 operate at about 2% slip while the synchronous motors 13 and 14 are operating at synchronism from the 64 cycle alternator 19. With these pole numbers the speeds ofall the motors are at the correct amount and equal 160 revolutions per minute. The synchronous speed of the induction motors 15 and 16 would be about three revolutions higher than this. a

I For low speed operation the low speed alternator 20 is connected to the synchronous motors 13 and 14 and disconnected from the induction motors 15 and 16. The high freuency alternator 19 is likewise disconnected.

his may be readily performed by. appropriately manipulatin switches 17, 18 and 23. Should the turbine 22 be operating at its normal full speed, then the alternator 20 would be operating to supply power at 49 cycles to the synchronous motors. The speed of the propeller shafts would then be about 122 revolutions per minute and the power required would be approximately 58% of that required at top speed. The alternator 20 can properly be designed to take care of this. Somewhat higher speeds may be obtained by varying the speeds of the alternators. All maneuvering, such as going in and out of ports, reversing, etc., Would be done with the use of the synchronous motors 13 and 14 alone and connected to the low fre uenc source, and these motors would pre erab y be built with a high resistance squirrel cage winding on the periphery of the poles, so that they maybe used as induction motors for certain stages of the operation of the system.'

We have illustrated in Fig. 2 another means for preventing the flow of circulating currents between the motors having fewer poles when they are switched on the line in passin from low speed to high speed operation. n this embodiment the synchronous motors 13 and 14 are arranged as before and are adapted to be connected by means of switches 17 or 18 to either the high frequency alternator 19 or the -low frequency correspondin alternator 20. In this instance themotors 25 and 26 having 36 poles may be of the synchronous type. The low frequency source in this instance must have ,48 cycles in order that the speed of these motors 25 and 26 may be equal to the synchronous speed of the motors 13 and 14. Located between these two motors and directly mounted on the shafts 11 and 12 are means for keeping the motors 25 and 26 in synchronism while the motors 13 and 14 are in synchronism. These means comprise dynamo electric machines 27 and 28 mounted on the shafts 11 and 12 and having stators 29 and 30 connected by a switch 31 so that their E. M. F.s go

.Preferably the highest number that fulfills this requirement should be used. Thus in the present instance these dynamo electric machines are wound for 6.po1es, each pole corresponding to 8 poles on machines 13 and 14 and 6 poles on machines 25'and 26. These dynamo electric machines tend to keep the propeller shafts 11 and 12 in synchronism as regards their own rotors, and if there is any tendency for one shaft to get out of step .the stators of these dynamo electric machines would have circulating currents produced in them which would exert a tor ue tending to bring these shafts back to sync ronism. All of the rotors on each shaft should be accurately aligned so that one pole member of machine 27 will exactly coincide with a block of 8 poles of machine 13 and a block of 6 poles of machine 12 and further so that the alternate arrangements of north and south poles in each block are the same. The same observations hold as regards the three machines mounted on shaft 12. Since the rotor members of machines 27 and 28 must al-- ways be in synchronism when they are 116 active, it is evident that the rotor members of motors 25 and 26 must also always he in synchronism, since there are an even number of poles on machines 25 and 26 to one pole on the machines 120 27 and 28. hile all of the motors 13, 14, 25 and 26 are operating for high speed operation it is not necessary to provide excitation for machines 27 and 28, since then the two shafts 11 and 12 are maintained in synchronism by the parallel'connection of the motors. During the change-over, however, from low speed to high speed, excitation is supplied to these machines 27 and 28 so as to bring the shafts into synchronism before mo-v tors 25 and 26 are connec d to the source 20.

illustrated in Fig. 2 is operated in going from standstill to full s eed the followingexplanation is provided he low speed turbine 21 would be run at slow speed and switched on to motors 13 and 14 by means of switch 18. These motors are at the start provided with no excitation. Excitation would now be supplied to dynamo electric machines 27 and 28 and this would bring all of the machines into correct phase relationship. Excitation could now be sup lied to the motors 13 and 14 and taken 0 of the dynamo electric machines 27 and 28. The low speed turbine 21 could then be run up to its normal low speed value and if it were desired to .operate the ship at that speed no further manipulation is required. If it is required, however, to operate the ship at high speed, high speed alternator 19 would be started and run up to the same. speed as the alternator 20. The low frequency alternator 20 would then be disconnected from motors 13 and 14 and the high freuency alternator 19 would be connected t ereto by proper manipulation of switches 17 and 18. During this operation, excitation is supplied to the dynamo electric machines 27 and 28. The low fre uency alter- 'nator 20 would then berun at t e frequency thereto, but aim to embrace,in the ap corresponding to that-of motors 25' and 26 and switched on at low voltage. Now excitation for the motors 13, 14, 25 and 26 may be su plied and the turbines 21 and 22 accelerated to their normal full speed. Afterthis is accomplished the excitation for the machines 27 and 28 may be discontinued.

While we haveshown in the ,accompany ing drawings several embodiments of our invention, we do not wishto be limited pended claims all modifications falling fairly within the scope of our invention.

What we clalm as new and desire to secure by Letters Patent of'the United States, 1s

prising a pair of propeller shafts, a air of similar synchronous motors, each rivin separate propellerlshafts, a source of re atively high frequency alternating current,

a source of relatively Iowfrequency alter- 'natin a main motors,

current, means for connecting the high requency source to the pair of motors, auxiliary driving motors for the shafts arrangedtooperat'e. with fewer polesthan the and to be connected with the low frequency source, and means whereby the auxiliary"motors are kept in synchronism while the main motors are in synchronism.

2. An electric ship-propulsion system comprising a pair of propeller shafts, a pair of similar synchronous motors, each mounted on separate shafts, a source of relatively high frequency alternating current, a source of relatively low frequency alternating current, means for connecting said motors in parallel to the high frequency source another pair of driving motors each having a rotor and the rotors mounted on separate shafts, said latter motors having fewer poles than the other motors and means for connecting said motors in parallel to the low. frequency source, the arrangement being such that when the synchronous motors are synchronized, the rotors of the second pair of motors are likewise in synchronism, whereby there can be no appreciable circulating currents between the second pair of motors.

3. An electric ship propulsion system comprising a pair of propeller shafts, a pair of similar synchronous motors, each directly driving separate propeller shafts, a source of relatively high frequenc alternating current, a source of relativelgy low frequency alternating current, means for connectlng in the same ratio as the frequencies of the low and high frequency source, and means for insuring synchronism of the motors with fewer poles while the other motors are in synchronism comprising a dynamo electric machine on each shaft, having an armature member and a field member of such a number of poles that there is an even number "of oles on allof the motors for each of the po es on this field member, said armature members being adapted for connection in opposition to each other.

4. In an electric ship propulsion system comprising two alternators, one operated by a low speed primemover and the other by a high speed prime mover, two propeller shafts each havmg a .plurality of synchronous 1. An electric ship propulsion systemcom motors of differing pole numbers, the motors electric machine on each' shaft having an armature and a field member of such a number of poles that there is an even number of alternator having a let er pole number being furnished with squirre cage windings, and a dynamo mover, supplying excitation to the field memnator to its normal value, and connecting the hem of the dynamo electric machines, conlow speed alternator to the motors with necting their a'rmatures in opposition, supthe fewer poles.

plying field excitation to the operating syn- In witness whereof, we have hereunto set 5 chronous motors, gradually speeding up the our hands this twenty-sixth day of Febalternator supplying the motors to its norruary, 1921.

mal speed, running the high speed alternator at the speed of the active alternator, discon- JOHN MARTIN.

necting the first alternator, connecting the FRED'lH OLOUGH' 10 high speed alternator to the synchronous Witnesses: motors with large pole numbers, gradually N. EDWARD WALLIN,

I increasing the speed of the high speed alter- J. FOSTER. 

